Current chip packages may have poor heat dissipation. FIG. 9A shows an illustration of heatsink-isolation based on molding. A chip package, e.g. a transistor outline (TO) chip package, may include a back side isolation, e.g. an encapsulation material, e.g. a mold compound, formed over a back side of a leadframe as indicated by 909, wherein back side isolation having typical thicknesses may result in a worse heat dissipation performance than a TO chip package without a back side isolation. FIG. 9B shows the thermal resistance 919 (K/W) with respect to chip area 921 (mm2) of a chip package with different back side isolation thicknesses: no back side isolation 911; about 400 μm thick back side isolation 913; about 600 μm thick back side isolation 915; and about 800 μm thick back side isolation 917. Typical encapsulation thicknesses of the back side isolation, which are normally around 400 μm, e.g. as shown by 913, suffer from a much larger thermal resistance than chip packages without back side isolation, e.g. as shown by 911, and therefore exhibit poorer heat dissipation than without back side isolation.
FIG. 5 shows a graph 500 of dielectric break down strength (kV/mm) 519 versus sample thickness d 521, e.g. a mold compound thickness. FIG. 5 shows that for a range of materials, the dielectric breakdown strength decreases as the thickness of the material increases. As a result, chip packages with a thick back side isolation layers, e.g. thick mold compounds, may result in a reduced dielectric breakdown strength.
FIGS. 10A and 10B show a chip package, e.g. a Fullpak chip package, wherein a chip 1006 may be formed on a leadframe. The leadframe may be insulated at its back side 309 with mold compound 1007. A bond wire 1008 may be electrically connected to the chip and to the leadframe 1005, and wherein at least part of the leadframe may be plated 1009. The lead frame may function as a heat sink for the components, and may be molded with mold compound on the back side 309 using an encapsulation process. A 100 μm thick mold compound for example, may be formed over the lead frame back side 309 and the chip back side. Therefore, the leadframe may be molded on both sides. The leadframe may extend through the mold compound, wherein the leadframe back side 309 may be electrically insulated from the environment.
As shown in FIG. 10B, limited electrical insulation may be achieved with the mold compound 1007 due to cracks 1011 and/or voids 1013 in the mold compound, which may significantly affect the electrical insulating performance. Further challenges are associated with the application of mold compound and costs. Furthermore, mold compounds offer a low thermal conductivity of less than 1 W/mK.